Droplet forming method for mixed liquid and droplet forming device, and ink jet pringting method and device, and ink jet pringing electrode-carrying nozzle

ABSTRACT

The invention provides an ink jet printing method for printing a color image on a printing object by using a plurality of inks, wherein ink nozzles  9   a  through  9   d  which house the plurality of inks, respectively, and a dilution nozzle  8  which houses a dilute solution that can dilute the inks are used, the ink is discharged from the ink nozzle  9   a  by an electrostatic sucking force to form a droplet L on a printing object  4 , and then the ink is discharged from the ink nozzle  9   b  by an electrostatic sucking force and the inks are mixed within the droplet L to form a droplet in an arbitrary additive color. In this case, primary color inks can be accurately mixed within the droplet L.

TECHNICAL FIELD

The present invention relates to mixture droplet forming method andapparatus, ink jet printing method and apparatus, and an ink jetprinting electrode-attached nozzle.

BACKGROUND ART

Generally, an ink jet printing apparatus forms color images by stampingthree primary color inks (C (cyan), M (magenta), and Y (yellow))corresponding to three primary colors or four primary color inks(including K (black) in addition to the C, M, and Y) onto a printingobject, and expresses additive colors by changes in dot density.

However, in expression of additive colors by changes in dot density, asubtle color cannot be satisfactorily expressed or a resultant imageprovides a sense of roughness.

As an inkjet printing apparatus solving this problem, for example, oneis disclosed in Patent Document 1: Japanese Published Unexamined PatentApplication No. H08-207318 as described below.

FIG. 7 is a schematic sectional view showing the ink jet printingapparatus described in the same publication. This ink jet printingapparatus 100 applies a voltage between a ring-shaped electrode 101 andan electrode plate 102 by a power supply 108, discharges a concentratedink 104 from a liquid feed pipe 103, and forms a droplet made of the inkon a printing object 105 on the electrode plate 102. When adjusting theink density, the concentrated ink 104 is sucked out of the liquid feedpipe 103, and simultaneously, a transparent solvent 107 is sucked out ofthe liquid feed pipe 106 and the concentrated ink is diluted by thetransparent solvent, and the diluted droplet is discharged to form adroplet the ink density of which has been adjusted on the printingobject 105.

[Patent Document 1]

Japanese Published Unexamined Patent Application No. H08-207318

DISCLOSURE OF THE INVENTION

However, the ink jet printing apparatus 100 described in theabove-mentioned conventional published application has the followingproblem.

That is, in the ink jet printing apparatus 100, a liquid that is cut offand left on the liquid feed pipe 103 side after being discharged is amixed liquid of the concentrated ink and the transparent solvent, andthe mixed liquid remains inside the liquid feed pipe 103. Therefore,when this remaining liquid and other color ink are mixed thereafter, anunintended color is printed on the printing object. Therefore, in themethod for adjusting the ink density as described above, it is difficultto realize an accurate subtle color.

Therefore, an object of the invention is to provide a mixed liquiddroplet forming method and apparatus, an ink jet printing method andapparatus, and an ink jet printing electrode-attached nozzle, by whichliquids to be discharged independently from each nozzle can beaccurately mixed on a droplet forming object.

In order to solve the above-mentioned problem, the invention provides amixed liquid droplet forming method comprising a first step in which avoltage is applied first between a raw material liquid housed in one ofa plurality of nozzles and a flat electrode disposed opposite the nozzleto discharge the raw material liquid from the front end of the nozzleand form a droplet made of the raw material liquid on a droplet formingobject disposed between the front end of the nozzle and the flatelectrode, and a second step in which a voltage is applied between a rawmaterial liquid housed in the other nozzle of the plurality of nozzlesand the flat electrode to discharge the raw material liquid from thefront end of the nozzle, and the droplet is mixed with the raw materialliquid to form a droplet of the mixed liquid.

According to this invention, a voltage is applied first between a rawmaterial liquid housed in one of the plurality of nozzles and the flatelectrode and the raw material liquid is discharged from the front endof the nozzle to form a droplet made of the raw material liquid on adroplet forming object. At this point, due to the existence of thedroplet, the equipotential line becomes convex toward the nozzle side.Therefore, when a voltage is applied between a raw material liquidhoused in the other nozzle and the flat electrode, the electrical fieldbecomes greater along the line connecting the raw material liquid andthe droplet. Therefore, when the raw material liquid housed in the othernozzle is discharged, the raw material liquid is guided to this droplet,and the raw material liquids are accurately mixed within the droplet.

Preferably, in the first step, an electrode is provided on the outercircumference of at least one nozzle of the plurality of nozzles and theelectrode is supplied with a potential equal to or higher than thepotential of a raw material liquid inside the nozzle.

In this case, the electrical line of force concentrates immediatelyunder the nozzle provided with the electrode, so that it becomespossible to accurately dispose the raw material liquid at a desiredposition on the droplet forming object. Therefore, when the raw materialliquid is discharged toward the droplet forming object, the raw materialliquid can be accurately mixed with the droplet on the droplet formingobject. Furthermore, raw material liquids are not mixed before they aredischarged but are mixed after they are discharged. Accordingly, thequalities of the raw material liquids do not change inside the nozzles.Therefore, even when a droplet is repeatedly formed on the dropletforming object, a droplet with an intended quality can be formed as onedot.

In addition, the invention provides a mixed liquid droplet formingapparatus, comprising a plurality of nozzles that house a plurality ofraw material liquids and discharge the plurality of raw material liquidsindependently from each other, a flat electrode disposed opposite thefront ends of the plurality of nozzles, and a voltage applying unit thatapplies a voltage between raw material liquids housed in the pluralityof nozzles and the flat electrode.

According to this droplet forming apparatus, when a voltage is appliedbetween a raw material liquid housed in one of the plurality of nozzlesand the flat electrode by the voltage applying unit, the raw materialliquid is discharged from the nozzle to form a droplet on the dropletforming object. At this point, due to the existence of the droplet, theequipotential line becomes convex toward the nozzle side. Therefore,when a voltage is applied between a raw material liquid housed in theother nozzle and the flat electrode, the electrical field becomesgreater along the line connecting this raw material liquid and thedroplet. Therefore, when the raw material liquid housed in the othernozzle is discharged, this raw material liquid is guided to this dropletand the raw material liquids are accurately mixed within this droplet.

The mixed liquid droplet forming apparatus may further comprise acontrol unit that controls the voltage applying apparatus so that avoltage is applied to an arbitrary raw material liquid among theplurality of raw material liquids.

Preferably, in the mixed liquid droplet forming apparatus, an electrodeis provided on the outer circumference of at least one nozzle of theplurality of nozzles, and the control unit controls the voltage applyingunit so that the electrode is supplied with a potential equal to orhigher than the potential of the raw material liquid.

In this case, when the voltage applying unit is controlled by thecontrol unit so as to supply a potential higher than the potential ofthe raw material liquid to the electrode, the electrical line of forcefurther concentrates immediately under the nozzle. Therefore, it becomespossible to dispose the raw material liquid at a desired position on thedroplet forming object. Therefore, after that, when the raw materialliquid is discharged toward the droplet forming object, it can beaccurately mixed with the droplet made of a raw material liquid.Furthermore, the raw material liquids are not mixed before they aredischarged from the nozzles but are mixed on the droplet forming objectafter they are discharged, so that the qualities of the raw materialliquids are not changed inside the nozzles. Therefore, a droplet with anintended quality can be formed as one dot.

According to an ink jet printing method relating to the invention, theink jet printing method for printing a color image on a printing objectby using a plurality of inks, comprises a first step in which aplurality of ink nozzles which house the plurality of inks and adilution nozzle which houses a dilute solution that can dilute the inksare used, and the ink or the dilute solution is discharged from the inknozzles or the dilution nozzle by an electrostatic sucking force to forma droplet on the printing object, and a second step in which the ink orthe dilute solution is discharged from the ink nozzle or the dilutionnozzle by an electrostatic sucking force, and the inks or the dilutesolution are mixed in the droplet to form a droplet in an additivecolor.

According to this invention, first, a voltage is applied between the inkor the dilute solution housed in one of the ink nozzles and the dilutionnozzle and the flat electrode, and the ink or dilute solution isdischarged from the front end of the ink nozzle or dilution nozzle toform a droplet made of the primary color ink or dilute solution on aprinting object. At this point, due to the existence of the droplet, theequipotential line becomes convex toward the nozzle side. Therefore,next, when a voltage is applied between the ink or dilute solutionhoused in the other nozzle and the flat electrode, the electrical fieldbecomes great along the line connecting this ink or dilute solution andthe droplet. Therefore, when the ink or dilute solution housed in theother nozzle is discharged, this liquid is guided to this droplet, andthe inks or the ink and the dilute solution are accurately mixed withinthis droplet, whereby a droplet in an additive color is formed.

Preferably, in the first step, a droplet made of the dilute solution isformed on a printing object by discharging the dilute solution from thedilution nozzle.

In this case, when the ink is mixed with the droplet after the secondstep, color change of the droplet due to proceeding with the colormixture can be easily judged.

Preferably, after the second step, the method further comprises a stepin which the chroma of the droplet is measured, and based on themeasured chroma, the quantity of discharging the inks or the dilutesolution is controlled so that the chroma of the droplet becomes adesired chroma.

In this case, a target additive color can be accurately expressed.

Preferably, in the ink jet printing method, an electrode is provided onthe outer circumference of the dilution nozzle and the electrode issupplied with a potential equal to or higher than the potential of thedilute solution inside the dilution nozzle.

In this case, since the electrical line of force concentratesimmediately under the dilution nozzle, the dilute solution can beaccurately disposed at a desired position on a printing object.Therefore, after that, when the ink is discharged to the printingobject, it can be accurately mixed with the droplet made of the dilutesolution. Furthermore, the dilute solution and the ink are not mixedbefore they are discharged but are mixed on the printing object afterthey are discharged. Therefore, inks do not change in quality in therespective ink nozzles. Therefore, even when a droplet is repeatedlyformed, a droplet in an intended additive color can be formed as onedot, and printing with high accuracy without distortion is realized.

According to the ink jet printing apparatus of the invention, the inkjet printing apparatus for printing a color image on a printing objectby using a plurality of inks, comprises a dilution nozzle which houses adilute solution that can dilute the inks, a flat electrode disposedopposite the front ends of the ink nozzles and the dilution nozzle, anda voltage applying unit which applies a voltage between the inks and thedilute solution and the flat electrode, wherein the plurality of inknozzles and the dilution nozzle are disposed apart from each other.

According to this ink jet printing apparatus, when a voltage is appliedbetween the ink or dilute solution and the flat electrode by the voltageapplying unit, the ink or dilute solution is discharged from the inknozzle or dilution nozzle to form a droplet on a printing object. Atthis point, due to the existence of the droplet, the equipotential linebecomes convex toward the nozzle side. Therefore, when a voltage isapplied between the ink or dilute solution housed in the other nozzleand the flat electrode, the electrical field becomes greater along theline connecting the ink or dilute solution and the droplet. Therefore,when the ink or dilute solution housed in the other nozzle isdischarged, this liquid is guided to this droplet, and the inks or theink and the dilute solution are accurately mixed within this droplet,whereby a droplet in an additive color is formed.

The ink jet printing apparatus may further comprise a control unit whichcontrols the voltage applying unit so that a voltage is applied to anarbitrary liquid among the inks and the dilute solution.

Preferably, in the ink jet printing apparatus, an electrode is providedon the outer circumference of the dilution nozzle, and the control unitcontrols the voltage applying unit so that the electrode is suppliedwith a potential equal to or higher than the potential of the dilutesolution.

In this case, when the voltage applying unit is controlled by thecontrol unit so as to supply a potential equal to or higher than thepotential of the dilute solution to the electrode, the electrical lineof force further concentrates immediately under the dilution nozzle.Therefore, it becomes possible to dispose the dilute solution at adesired position on the printing object. Therefore, after that, when theink is discharged toward the printing object, it can be accurately mixedwith the droplet made of the dilute solution. Furthermore, the dilutesolution and the ink are not mixed before they are discharged from thenozzles but are mixed on the printing object after they are discharged,so that the ink densities do not change in the ink nozzles. Therefore, adroplet in an intended additive color can be formed as one dot, wherebyprinting with high accuracy without distortion is realized.

Preferably, the ink jet printing apparatus further comprises anilluminating light source which illuminates a droplet formed on theprinting object, and a chroma measuring unit which measures the chromaof the droplet illuminated by the illuminating light source, wherein thecontrol unit controls the voltage applying unit based on the chroma ofthe droplet measured by the chroma measuring unit so that the chroma ofthe droplet becomes a desired chroma and adjusts the quantity ofdischarging the ink or the dilute solution.

In this case, a target additive color can be accurately expressed.

Furthermore, according to the invention, an ink jet printingelectrode-attached nozzle which is used in an ink jet printing apparatusincluding a flat electrode and disposed opposite the flat electrode,comprises a nozzle housing an ink or dilute solution and an electrodeprovided on the outer circumference of the nozzle.

According to this ink jet printing electrode-attached nozzle, when it isused in an ink jet printing apparatus including a flat electrode, aprinting object is disposed between the nozzle and the flat electrode, avoltage is applied between an ink or dilute solution housed in thenozzle and the flat electrode, and furthermore, the electrode issupplied with a potential equal to or higher than that of the ink or thedilute solution, whereby the electrical line of force furtherconcentrates immediately under the electrode-attached nozzle, andtherefore, the ink or dilute solution can be accurately disposed at adesired position on the printing object. Therefore, after that, when theink or dilute solution is discharged to the printing object, it can beaccurately mixed with the droplet on the printing object.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view showing a main part of anembodiment of the ink jet printing apparatus of the invention;

FIG. 2 is a bottom view of a nozzle head;

FIG. 3 is a partial sectional view of a dilution nozzle;

FIG. 4A, FIG. 4B, and FIG. 4C are timing charts of pulse voltages innozzles;

FIG. 4D, FIG. 4E, FIG. 4F, FIG. 4G, and FIG. 4H are views showing aseries of processes for forming a droplet in an additive color,respectively;

FIG. 5 is a flowchart showing processes for accurately realizing anintended additive color;

FIG. 6 is a schematic sectional view showing a main part of anotherembodiment of the ink jet printing apparatus of the invention;

FIG. 7 is a schematic sectional view showing an example of aconventional ink jet printing apparatus.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the invention are described in detail.

FIG. 1 is a schematic view showing a main part of an embodiment of theink jet printing apparatus of the invention, and FIG. 2 is a bottom viewof a nozzle head.

As shown in FIG. 1, the ink jet printing apparatus 1 of this embodimenthas a nozzle head 2, and a flat electrode 3 is disposed opposite thenozzle head 2. On the flat electrode 3, a recording sheet (dropletforming object) 4 as a printing object is placed. The nozzle head 2 canbe made to reciprocate in the arrow A direction of FIG. 1 by a nozzlehead transport system 5, and the recording sheet 4 can be moved in thearrow B direction orthogonal to the arrow A direction by a chart drivemechanism 6.

As shown in FIG. 2 and FIG. 3, the nozzle head 2 has a nozzle holder 7,and in the nozzle holder 7, four ink nozzles 9 a, 9 b, 9 c, and 9 d (9 athrough 9 d) housing four primary color inks (raw material liquids) 9 a₁, 9 b ₁, 9 c ₁, and 9 d ₁ corresponding to four primary colors areinserted and fixed. A dilution nozzle 8 and the ink nozzles 9 a through9 d are made of glass in terms of dimensional stability. The fourprimary color inks 9 a ₁, 9 b ₁, 9 c ₁, and 9 d ₁ are C (cyan), M(magenta), Y (yellow), and K (black), and the ink nozzles 9 a through 9d house the C ink 9 a ₁, M ink 9 b ₁, Y ink 9 c ₁, and K ink 9 d ₁,respectively. The dilution nozzle 8 is connected to a dilute solutionsupply tank (not shown), and the ink nozzles 9 a through 9 d areconnected to ink supply tanks (not shown).

The ink nozzles 9 a through 9 d and the dilution nozzle 8 are disposedapart from each other. In detail, the dilution nozzle 8 is fixed to thecenter of the nozzle holder 7, and the ink nozzles 9 a through 9 d aredisposed at equal intervals in a circle around the dilution nozzle 8.Disposition of the dilution nozzle 8 at the center is for dischargingthe dilute solution first among the primary color inks and the dilutionsolution when forming one dot of droplet on the recording sheet 4.Therefore, when other primary color ink is discharged first when formingone dot of droplet on the recording sheet 4, this primary color ink isdisposed at the center.

Furthermore, as shown in FIG. 1, the inks and the dilute solution housedin the ink nozzles 9 a through 9 d and the dilution nozzle 8 areelectrically connected to the flat electrode 3 via a voltage applyingunit 10 that can supply pulse voltages. Therefore, by the voltageapplying unit 10, between the inks or the dilute solution and the flatelectrode 3, voltages are applicable.

In the nozzle holder 7, an illuminating fiber 11 and a light receivingfiber 12 are inserted and fixed at positions axisymmetrical to eachother about the dilution nozzle 8 (see FIG. 2). The illuminating fiber11 is connected to a white light source (illuminating light source) 13,and the light receiving fiber 12 is connected to a chroma measuring unit14 (see FIG. 1). Therefore, it becomes possible to illuminate a dropletby white light from the white light source 12 through the illuminatingfiber 11, and light received from the droplet through the lightreceiving fiber 12 is received by the chroma measuring unit 14, and thechroma of the droplet is measured based on this light.

Furthermore, the ink jet printing apparatus 1 has a control unit 15, andby the control unit 15, the nozzle head transport system 5, the chartdrive mechanism 6, the voltage applying unit 10, the white light source13, and the chroma measuring unit 14 can be controlled.

Next, an ink jet printing method using the above-described ink jetprinting apparatus 1 is described with reference to FIG. 3 and FIG. 4Athrough FIG. 4H.

FIG. 3 is a partial sectional view of the dilution nozzle, showing acondition where a dilute solution is discharged from the dilution nozzleand a droplet is formed on the recording sheet 4. In FIG. 3, theconstruction of the dilution nozzle 8 is described, and the constructionand function of the dilution nozzle 8 are the same as those of the inknozzles 9 a through 9 d, and in this case, inside the ink nozzles 9 athrough 9 d, inks 9 a ₁ through 9 d ₁ are housed instead of the dilutesolution 8 a.

FIG. 4A, FIG. 4B, and FIG. 4C are timing charts of pulse voltages ΔE₃,ΔE₂, and ΔE₁ to be applied between the nozzles and the flat electrode 3,and FIG. 4D, FIG. 4E, FIG. 4F, FIG. 4G, and FIG. 4H are views showing aseries of processes for forming a droplet in an additive color.

First, a pulse voltage is applied between the dilute solution and theflat electrode 3 by the voltage applying unit 10. At this point, asshown in FIG. 4B, a pulse voltage is formed by applying a voltage ΔE₂between the timings t₁ and t₂. Then, as shown in FIG. 3 and FIG. 4D, thedilute solution 8 a is sucked out of the dilution nozzle 8 byelectrostatic sucking force to form a Taylor Cone 16, and then apredetermined quantity of the dilute solution is discharged and adroplet L made of the dilute solution is formed on the recording sheet4.

Next, a voltage is applied between the Y ink stored in the ink nozzle 9c and the flat electrode 3 by the voltage applying unit. At this point,as shown in FIG. 4A, between the timings t₂ and t₃, a pulse voltage isformed by applying the voltage ΔE₃. At this point, due to the existenceof the droplet formed on the recording sheet 4, the equipotential lineis convex toward the nozzle 9 c side, and the electrical field becomesgreater along the line connecting the front end of the ink nozzle 9 cand the droplet.

Therefore, as shown in FIG. 4E, the Y ink is sucked out of the inknozzle 9 c by an electrostatic sucking force and forms a Taylor Cone,and then a predetermined quantity of the Y ink is discharged toward thedroplet L. The Y ink causes turbulence when it enters in the droplet,whereby the Y ink and the dilute solution are mixed accurately.

At this point, as shown in FIG. 4F, the droplet L is illuminated bywhite light emitted from the white light source 13 through theilluminating fiber 11, and light emitted from the droplet L is receivedby the chroma measuring unit 14 through the light receiving fiber 12.Then, based on the chroma measured by the chroma measuring unit 14, anaddition quantity of the Y ink or the dilute solution is adjusted sothat the chroma of the droplet L becomes a desired chroma. In detail,this addition quantity is adjusted by the pulse period of the pulsevoltage outputted from the voltage applying unit 10.

Next, a voltage is applied between the C ink housed in the ink nozzle 9a and the flat electrode 3 by the voltage applying unit 10. At thispoint, as shown in FIG. 4C, between the timings t₃ and t₄, a pulsevoltage is formed by applying the voltage ΔE₁. At this point, due to theexistence of the droplet L formed on the recording sheet 4, theequipotential line is convex toward the ink nozzle 9 a side, andtherefore, the electrical field becomes greater along the lineconnecting the front end of the ink nozzle 9 a and the droplet L.Therefore, as shown in FIG. 4G, the C ink is sucked out of the inknozzle 9 a by an electrostatic sucking force and forms a Taylor Cone,and then a predetermined quantity of the C ink is discharged toward thedroplet L. The C ink causes turbulence when it enters the inside of thedroplet L, whereby the C ink and the dilute solution are accuratelymixed.

At this point, as shown in FIG. 4H, the droplet L is illuminated bywhite light emitted from the white light source 13 through theilluminating fiber 11, and light emitted from the droplet L is receivedby the chroma measuring unit 14 through the light receiving fiber 12.Then, in the same manner as described above, based on the chromameasured by the chroma measuring unit 14, the addition quantity of the Cink or the dilute solution is adjusted so that the chroma of the dropletL becomes a desired chroma.

Thereafter, the M ink and the K ink are injected into the droplet L asappropriate to form a droplet L in an additive color. The method forinjecting the M ink and the K ink is the same as that for the Y ink.When forming a droplet L in an additive color, it is preferable that thecolor is gradually made darker from a light color, and a color with atarget chroma is finally reached. Thereby, judgement on changes in colorby chroma measurement can be made easily.

A droplet L in an additive color is thus formed on the recording sheet4. This droplet L in the additive color is formed by mixture of primarycolor inks, however, mixture of primary color inks is not carried outbefore the inks are discharged from the nozzles, but is carried outafter they are discharged. Therefore, the densities of the primary colorinks housed in the ink nozzles 9 a through 9 d are always maintainedconstant. Therefore, even when the ink jet printing apparatus 1 isrepeatedly used, a droplet L formed on the recording sheet 4 can beaccurately provided with an intended additive color.

After forming a droplet, the recording sheet 4 is moved in the arrow Bdirection of FIG. 1 by the chart transport system 6 or the nozzle head 2is moved in the arrow A direction of FIG. 1 by the nozzle head transportsystem 5, a droplet is formed in the same manner as described above, andthis operation is repeated, whereby a color image using real colorsinstead of false colors can be formed. The operations of theabove-described nozzle head transport system 5, the chart transportsystem 6, the voltage applying unit 10, the white light source 13, andthe chroma measuring unit 14 may be all controlled by the control unit15.

Herein, for providing a droplet L with an intended additive color moreaccurately, it is preferable that the degree of color mixture of thedroplet L is judged every time each ink is injected into the droplet L.

In detail, the following operation is carried out for judging the degreeof color mixture of the droplet L.

Namely, the droplet L is illuminated by white light first, and thechroma of the droplet L is measured by using the chroma measuring unit14. Next, the measured chroma is converted and a brightness index L*according to the CIELAB color system and chroma coordinates a* and b*are calculated.

However, in this case, previous to color mixture, it is necessary thatthe mixture ratio of the primary color inks for realizing the targetadditive color and the values of L*, a* and b* of the primary color inksaccording to the ratio are prepared based on the data of the absorptionspectra of the primary color inks.

Herein, an example of the process realizing the target additive color byjudging the degree of color mixture of the droplet based on the measuredchroma is described.

FIG. 5 is a flowchart for realizing the target additive color. As shownin FIG. 5, first, a droplet L made of a dilute solution is formed on therecording sheet 4 (Step 1).

Next, by setting the values of L*, a*, b* with respect to the targetadditive color as judgement criteria, it is judged whether the degree ofmixture of the Y ink is high or low. If the degree is low, a unitquantity of the Y ink is added, and if the degree is high, a unitquantity of the dilute solution is added (Step 2). Herein, the unitquantity means the quantity of ink or dilute solution to be dischargedwhen a voltage of one pulse is applied between the ink or dilutesolution and the flat electrode 3.

Next, the values of L*, a*, and b* of the C-Y mixed ink with respect tothe target additive color are set as judgement criteria, and it isjudged whether the degree of mixture of the C ink is high or low. If itis low, a unit quantity of the C ink is added, and if it is high, a unitquantity of the dilute solution is added (Step 3).

Next, the values of L*, a* and b* of C-M-Y mixed ink with respect to thetarget additive color are set as judgement criteria, and it is judgedwhether the degree of mixture of the M ink is high or low. If it is low,a unit quantity of the M ink is added, and if it is high, a unitquantity of the dilute solution is added (Step 4).

Last, accurate values of L*, a*, and b* with respect to the targetadditive color are set as judgement criteria, and it is judged whetherthe degree of mixture of the K ink is high or low. If it is low, a unitquantity of the K ink is added, and if it is high, a unit quantity ofthe dilute solution is added (Step 5).

Thus, the chroma of the droplet is measured every time an ink isinjected into the droplet, and color mixture is carried out while thedegrees of mixture of colors are judged, whereby the droplet L can beaccurately provided with the target additive color.

Next, a second embodiment of the ink jet printing apparatus of theinvention is described with reference to FIG. 6. In FIG. 6, componentsidentical or equivalent to those of the first embodiment are attachedwith the same symbols and description thereof is omitted.

As shown in FIG. 6, the ink jet printing apparatus of this embodiment isdifferent from the ink jet printing apparatus 1 of the first embodimentin that the dilution nozzle (electrode-attached nozzle) that has anelectrode 20 on its outer circumference is provided.

Herein, the material forming the electrode 20 is not especially limitedas long as it has conductivity, however, such a material is preferablygold or platinum in terms of corrosion proof. The electrode 20 is formedby, for example, depositing the material on the front end of thedilution nozzle 8.

In the ink jet printing apparatus of this embodiment, to form thedroplet L, the same voltage as the pulse voltage applied between, forexample, the dilute solution 8 a and the flat electrode 3 is appliedbetween the electrode and the flat electrode 3.

Then, the electrostatic inductive charge 21 appearing at the front endof the electrode 20 biases the charge distribution of the electrostaticinductive charge 161 on the surface of the dilute solution so that thedistribution becomes highest at the center of the nozzle, so that agreat electrostatic force acts on the portion with the high chargedensity, that is, between the center of the dilute solution surface andthe flat electrode 3. As a result, the Taylor Cone 16 stays within theinner diameter portion of the nozzle end face, and the form thereof isdeformed to be more acute. This is a result of concentration of theelectrical line of force on the nozzle center portion. Therefore, theposition where the droplet L is formed can be extremely stabilized. Inother words, the droplet L can be accurately formed at a desiredposition on the recording sheet 4.

After the droplet L is formed on the recording sheet 4, since primarycolor inks can be accurately injected to the droplet L in the ink jetprinting apparatus of this embodiment, a droplet L in an additive colorcan be accurately formed at a desired position. At this point, in thedroplet L, a plurality of droplets do not express one additive color,but the droplet itself, that is, one dot expresses an additive color.Therefore, by the ink jet printing apparatus of this embodiment, a colorimage with high accuracy without distortion can be printed.

Furthermore, according to the ink jet printing apparatus of thisembodiment, although the Taylor Cone 16 is formed, it stays within theinner diameter portion of the nozzle, the front end portion thereofbecomes acute, and liquid can be quickly cut off when it is discharged.Therefore, the distance between the dilute solution 8 a and the flatelectrode 3 can be shortened, and driving is carried out even by acomparatively small voltage. This effect eliminates the possibility ofdischarge between the dilute solution 8 a and the flat electrode 3, andimproves the reliability of the ink jet printing apparatus. Furthermore,by shortening the distance between the nozzle front end and the flatelectrode 3, downsizing of the ink jet printing apparatus also becomespossible.

Furthermore, by the ink jet printing apparatus of this embodiment, inaddition to the above-described effect, on-demand printing is alsopossible. Therefore, the ink jet printing apparatus of this embodimentis extremely effective as a micro printing apparatus of anticounterfeitprinting technology.

In the above-described embodiment, the same voltage as the pulse voltageapplied between the dilute solution and the flat electrode 3 is appliedbetween the electrode 20 and the flat electrode when forming thedroplet, however, it is preferable that a voltage greater than the pulsevoltage applied between the dilute solution and the flat electrode 3 isapplied between the electrode 20 and the flat electrode 3. In this case,the electrostatic inductive charge 21 appearing at the front end of theelectrode 20 biases the charge distribution of the electrostaticinductive charge 161 on the dilute solution surface so that thedistribution becomes highest at the nozzle center portion, so that agreat electrostatic force acts on the portion with the high chargedensity, that is, between the center portion of the dilute solutionsurface and the flat electrode 3. Therefore, the position where thedroplet is formed can be further stabilized, and a color image with highaccuracy without distortion can be printed.

In the above-described embodiment, the electrode 20 is provided for onlythe dilution nozzle 8, however, it is preferable that the electrode 20is also provided for the ink nozzles 9 a through 9 d. In this case, theouter circumferences of the front ends of the ink nozzles 9 a through 9d are provided with electrodes 20, and the construction and functionthereof are those obtained by substituting the dilution nozzle 8 shownin FIG. 6 with the ink nozzles 9 a through 9 d. With these ink nozzles 9a through 9 d, when the primary color inks 9 a ₁ through 9 d ₁ aredischarged, smaller unit quantities of the primary color inks made ofliquids that can be quickly cut off can be injected into the droplet L.

The invention is not limited to the above-described first and secondembodiments. For example, the first and second embodiments relate to inkjet printing apparatuses and use primary color inks or dilute solutionas raw material liquids, however, as raw material liquids, the mixedliquid droplet forming apparatus of this embodiment can also use aconductive liquid (for example, a silver paste or mercury) instead ofthe primary color inks and dilute solution. In this case, liquidsindependently discharged from the respective nozzles can be accuratelymixed on a droplet forming object. Furthermore, this conductive liquiddroplet forming apparatus functions as an apparatus for forming finetwo-dimensional electrical circuits (electrical wires, resistors,capacitors, reactance, and so on). As the raw material liquid, aninsulating liquid such as silicon oil or machine oil, etc., may be usedinstead of the conductive liquid.

As described above, according to the mixed liquid droplet forming methodand forming apparatus of the invention, liquids independently dischargedfrom the nozzles can be accurately mixed on a droplet forming object.

Furthermore, according to the ink jet printing method and apparatus ofthe invention, primary color inks or dilute solution independentlydischarged from the nozzles can be accurately mixed on a printing objectand a droplet in an intended additive color can be accurately formed.

Furthermore, according to the ink jet printing electrode-attached nozzleof the invention, when it is an ink jet printing apparatus including aflat electrode, a printing object is disposed between the nozzle and theflat electrode, and a voltage is applied between an ink or dilutesolution housed in the nozzle and the electrode and a potential higherthan that of the ink or the dilute solution is supplied to theelectrode, whereby the electrical line of force further concentratesimmediately under the electrode-attached nozzle, so that it becomespossible to accurately dispose the ink or dilute solution at a desiredposition on the printing object. Therefore, when the ink or dilutesolution is discharged to the printing object thereafter, it can beaccurately mixed with the droplet on the printing object.

Furthermore, in the chemical reaction in a liquid phase as a reactingfield, when carrying out reaction development and reaction analysis forcomposing a desired product from a plurality of raw material substances,for example, it is required that density dependency of each raw materialsubstance with respect to the yield of a desired product in probablereaction, density dependency of a catalyst (including enzymes), effectswhen using a different catalyst, and effects when using a differentsolvent are grasped and the reaction conditions are optimized.

In this case, for example, as in the case of drug screening inpharmaceutical development, enormous samples must be analyzed bychanging the reaction conditions. Therefore, in terms of operationefficiency improvement and cost reduction, technical development hasbeen considered for arranging many droplets of mixed liquids withdesired ingredient compositions orderly and quickly on predeterminedspots on a substrate as small quantities of droplets. In detail,technical development has been examined for a method in which rawmaterial liquids containing raw material substances and substancesrelating to reaction of the catalyst or the like are preparedindividually, and at the time of analysis, droplets of these are mixedin this situation at a predetermined volume ratio to instantaneouslyform droplets of mixed liquids with different ingredient compositions.

For example, Japanese Published Unexamined Patent Application No.2001-116750 discloses a method for manufacturing a reactive chipincluding a substrate on which substances (DNA fragments, cDNA,polypeptides, oligonucleotides, etc.) to be used as probes for DNAanalysis and the like are fixed by supplying predetermined quantities ofreactive substances (nucleotides, cDNA, DNA fragments, enzymes,antigens, antibodies, epitopes, or proteins, etc.) to predeterminedspots on the substrate at a high speed by using a plurality of ink jetnozzles and fixing these to the spot surfaces, and proposes a method forproducing the reactive substances by supplying raw materials of thereactive substances instead of the reactive substances on predeterminedspots on the substrate by using the similar method.

Namely, the raw material liquids to be housed in the above-mentionednozzles may be reactive substances (nucleotides, cDNA, DNA fragments,enzymes, antigens, antibodies, epitopes or proteins, etc.) in place ofthe inks.

In other words, the above-mentioned raw material nozzles 9 a, 9 b, 9 c,and 9 d are electrode-attached nozzles characterized by being providedwith electrodes on the outer circumferences of the front ends of thenozzles each housing a single raw material liquid, and by separatelyproviding a dilution nozzle 8 housing only a dilute solution apart fromthe raw material nozzles, the raw material liquids and the dilutesolution are discharged by a voltage applied between the electrodes 20and the flat electrode 3 and mixed on a droplet forming object.

INDUSTRIAL APPLICABILITY

The present invention can be used for a mixed liquid droplet formingmethod and apparatus, an ink jet printing method and apparatus, and anink jet printing electrode-attached nozzle.

1. A mixed liquid droplet forming method comprising: a first step inwhich a voltage is applied first between a raw material liquid housed inone of a plurality of nozzles and a flat electrode disposed opposite thenozzle to discharge the raw material liquid from the front end of thenozzle and form a droplet made of the raw material liquid on a dropletforming object disposed between the front end of the nozzle and the flatelectrode; and a second step in which a voltage is applied between a rawmaterial liquid housed in the other nozzle of the plurality of nozzlesand the flat electrode to discharge the raw material liquid from thefront end of the nozzle, and the droplet is mixed with the raw materialliquid to form a droplet of the mixed liquid.
 2. The mixed liquiddroplet forming method according to claim 1, wherein in the first step,an electrode is provided on the outer circumference of at least onenozzle of the plurality of nozzles and the electrode is supplied with apotential equal to or higher than the potential of a raw material liquidinside the nozzle.
 3. A mixed liquid droplet forming apparatus,comprising: a plurality of nozzles that house a plurality of rawmaterial liquids and discharge the plurality of raw material liquidsindependently from each other; a flat electrode disposed opposite thefront ends of the plurality of nozzles; and a voltage applying unit thatapplies a voltage between raw material liquids housed in the pluralityof nozzles and the flat electrode.
 4. The mixed liquid droplet formingapparatus according to claim 3, further comprising a control unit thatcontrols the voltage applying apparatus so that a voltage is applied toan arbitrary raw material liquid among the plurality of raw materialliquids.
 5. The mixed liquid droplet forming apparatus according toclaim 4, wherein an electrode is provided on the outer circumference ofat least one nozzle of the plurality of nozzles, and the control unitcontrols the voltage applying unit so that the electrode is suppliedwith a potential equal to or higher than the potential of the rawmaterial liquid.
 6. An ink jet printing method for printing a colorimage on a printing object by using a plurality of inks, comprising: afirst step in which a plurality of ink nozzles which house the pluralityof inks and a dilution nozzle which houses a dilute solution that candilute the inks are used, and the ink or the dilute solution isdischarged from the ink nozzle or the dilution nozzle by anelectrostatic sucking force to form a droplet on the printing object;and a second step in which the ink or the dilute solution is dischargedfrom the ink nozzle or the dilution nozzle by an electrostatic suckingforce, and the inks or the dilute solution are mixed in the droplet toform a droplet in an additive color.
 7. The ink jet printing methodaccording to claim 6, wherein in the first step, a droplet made of thedilute solution is formed on a printing object by discharging the dilutesolution from the dilution nozzle.
 8. The ink jet printing methodaccording to claim 6, further comprising, after the second step, a stepin which the chroma of the droplet is measured, and based on themeasured chroma, the quantity of discharging the ink or the dilutesolution is controlled so that the chroma of the droplet becomes adesired chroma.
 9. The ink jet printing method according to claim 7,wherein in the first step, an electrode is provided on the outercircumference of the dilution nozzle and the electrode is supplied witha potential equal to or higher than the potential of the dilute solutioninside the dilution nozzle.
 10. An ink jet printing apparatus forprinting a color image on a printing object by using a plurality ofinks, comprising: a plurality of ink nozzles which house the pluralityof inks, respectively a dilution nozzle which houses a dilute solutionthat can dilute the inks; a flat electrode disposed opposite the frontends of the ink nozzles and the dilution nozzle; and a voltage applyingunit which applies a voltage between the inks and the dilute solutionand the flat electrode, wherein the plurality of ink nozzles and thedilution nozzle are disposed apart from each other.
 11. The ink jetprinting apparatus according to claim 10, further comprising a controlunit which controls the voltage applying unit so that a voltage isapplied to an arbitrary liquid among the inks and the dilute solution.12. The ink jet printing apparatus according to claim 11, wherein anelectrode is provided on the outer circumference of the dilution nozzle,and the control unit controls the voltage applying unit so that theelectrode is supplied with a potential equal to or higher than thepotential of the dilute solution.
 13. The ink jet printing apparatusaccording to claim 11, further comprising: an illuminating light sourcewhich illuminates a droplet formed on the printing object; and a chromameasuring unit which measures the chroma of the droplet illuminated bythe illuminating light source, wherein the control unit controls thevoltage applying unit based on the chroma of the droplet measured by thechroma measuring unit so that the chroma of the droplet becomes adesired chroma and adjusts the quantity of discharging the ink or thedilute solution.
 14. An ink jet printing electrode-attached nozzle whichis used in an ink jet printing apparatus including a flat electrode anddisposed opposite the flat electrode, comprising an ink nozzle housingonly an ink and an electrode provided on the outer circumference of thenozzle.
 15. An ink jet printing electrode-attached nozzle which is usedin an ink jet printing apparatus including a flat electrode and disposedopposite the flat electrode, comprising a dilution nozzle that housesonly a dilute solution and an electrode that is provided on the outercircumference of the dilution nozzle.
 16. A nozzle which houses a singleraw material liquid, wherein an electrode is provided on the outercircumference of the front end of the nozzle.